In high voltage equipment, for example, molded transformers, switchgears, motors, and inverters, efficiency has been improved by reducing the size with a view point of energy saving and resource saving. In the high voltage equipment using insulation resins, reduction in the size results in problems of cracking and degradation of insulation due to reduction in the thickness of the film of the insulation resins. Accordingly, increase in the strength and in the withstanding voltage for the insulation resins are essential.
For increasing the strength and the withstanding voltage of the insulation resins, use of a resin material with addition of fine particles to resins is effective. Particularly, since fine particles of 1 to 100 nm diameter have a large surface area relative to the volume of the fine particle, improvement in the property of the resins is expected with a small addition amount.
For insulation resin materials with addition of fine particles to resins the following techniques have been known. JP-A No. 2005-241977 describes that stability with time of heat resistance, adhesion, and electric insulation is improved by the addition of a polyhydroxyl carboxylic acid ester additive and silica to a carboxyl group-containing resin. It is described that a thixotropic property is improved thereby improving the coating property of the resin, particularly, by the use of a hydrophilic silica.
JP-A No. 2008-31193 describes that modulus of elasticity, heat resistance, and toughness are improved by adding nano-particles and a block copolymer to an epoxy resin. It is described that the dispersibility of them to the epoxy resin is improved, particularly, by hydrophobizing the surface of inorganic nano particles.
JP-A No. H09 (1997)-326559 discloses a prepreg improved in the adhesion between a resin and a copper foil by adding a fiber base material, brucite, and super fine particles of silica to an epoxy resin. It is described that the dispersibility is improved, particularly, with hydrophobized silica.
It has been known that when particles are aggregated inside an insulation resin the mechanical strength and the withstanding voltage of the resin are not improved but they are improved by uniformly dispersing the fine particles in the resin. However, it has been found that when fine particle are dispersed uniformly, the mechanical property and the withstanding voltage of a hardened resin material are not improved and, particularly, resistance to crack propagation is not improved. Accordingly, distribution of fine particles inside the resin is one of main factors that determine the property of the resin. It is an important subject to determine the distribution of fine particles capable of improving the mechanical strength and the withstanding voltage, and define a combination of the fine particles and the resin capable of realizing such a distribution of the fine particles.
The above-mentioned patent documents do not select the combination of the fine particles and the resin material and not disclose the optimum constitution with the view points described above.
The present invention intends to improve the mechanical strength and the withstanding voltage of a resin material and provide high voltage equipment capable of improving the reliability by using the resin material of the invention to the high voltage equipment.